1. Field of the Invention
This invention relates to a drum type washing machine provided with means for detecting the weight of laundry accommodated in a drum.
2. Description of the Related Art
Conventional drum type washing machines comprise an outer cabinet, a water tub provided in the outer cabinet, a drum provided in the water tub so as to be rotated about a horizontal axis by an electric motor. In a conventional method of detecting the weight of laundry accommodated in the drum, displacement detecting means is provided for detecting an amount of displacement of the water tub vertically displacing according to the weight of laundry. The weight of the laundry is detected on the basis of the amount of displacement detected by the displacement detecting means. Further, another method has been suggested. In this method, rotational speed detecting means is provided for detecting a rotational speed of the motor or drum. When a rotational speed of the motor or drum is increased from zero to a predetermined value or decreased from a predetermined speed, a change in the rotational speed is detected. The weight of the laundry is detected on the basis of the change in the rotational speed of the motor or drum.
However, the cost of the washing machine is increased. In the latter method, the laundry weight detection takes a long time when the speed change is detected by driving the motor or drum at a high speed. On the other hand, when the speed change is detected by driving the motor or drum at a low speed, whether the laundry is one-sided in the drum, that is, a degree in the balance of the laundry adversely affect the change in the rotational speed of the motor or drum. As a result, the accuracy in the weight detection is reduced.
Therefore, an object of the present invention is to provide a drum type washing machine in which the detection of laundry weight can be carried out at a low cost with high accuracy.
The present invention provides a drum type washing machine comprising a drum for accommodating laundry and a variable speed electric motor for rotating the drum. Rotational speed detecting means is provided for detecting a rotational speed of the drum or the motor. Rise time detecting means is provided for detecting a rise time in a case where the drum or the motor is accelerated from a first predetermined rotational speed to a second predetermined rotational speed while a predetermined constant power is being supplied to the motor. Fall time detecting means is provided for detecting a fall time in a case where the drum or the motor is decelerated from a third predetermined rotational speed to a fourth predetermined rotational speed while the motor is in a free running state. Weight detecting means is provided for detecting a weight of the laundry in the drum on the basis of results of detection by the rise and fall time detecting means. Balance detecting means is provided for detecting a balance of the laundry in the drum. In the drum type washing machine, the weight detecting means compensates a result of detection according to a result of detection by the balance detecting means.
In the foregoing washing machine, the weight of the laundry in the drum is detected on the basis of the rise time and the fall time. This detecting manner can be realized by a lower cost than the detection of the displacement amount of the water tub. Moreover, the detecting accuracy can be rendered higher in the foregoing arrangement than in the case where the weight of the laundry is detected on the basis of either rise time or fall time. Further, the weight detecting means compensates the result of detection thereof according to the result of detection by the balance detecting means. Thus, since an error due to the balance of the laundry is added to the compensation, the detecting accuracy can further be improved. Additionally, a high accuracy is achieved even when the rise and fall times are detected on the basis of a low rotational speed of the motor or drum. Consequently, a detecting time can be reduced.
The drum type washing machine preferably further comprises control means for displaying an amount of a detergent to be used on the basis of the result of detection by the weight detecting means. Further, the balance detecting means preferably determines the balance on the basis of a ratio of the rise time and the fall time. Additionally, the drum type washing machine preferably further comprises rotational speed variation detecting means for detecting a rotational speed variation of the drum or the motor before the rise time is detected. In this arrangement, the weight detecting means compensates the result of detection on the basis of a result of detection by the rotational speed variation detecting means and the result of detection by the balance detecting means.